Part span shrouded fan blisk

ABSTRACT

Including a disk, a plurality of circumferentially spaced apart airfoils extending radially outwardly from the disk, a plurality of shroud segments being disposed circumferentially between the plurality of airfoils and configured to attach to a corresponding airfoil of the plurality of airfoils and a plurality of wear surfaces, where at least one wear surface of the plurality of wear surfaces is configured and disposed to prevent excessive wear between the adjacent shroud segments. Each shroud segment of the plurality of shroud segments may be attached to a corresponding airfoil by weld connections to permit clearance during translation friction welding of the airfoil to the disk hub are located to avoid high stress areas.

BACKGROUND OF THE INVENTION

In an aircraft gas turbine (jet) engine, air is drawn into the front of the engine, compressed by a shaft-mounted compressor, and mixed with fuel. The mixture is combusted, and the resulting hot combustion gas is passed through a turbine mounted on the same shaft. The flow of gas turns the turbine by contacting an airfoil portion of the turbine blade, which turns the shaft and provides power to the compressor. The hot exhaust gases flow from the back of the engine, driving it and the aircraft forward. There may additionally be a bypass fan that forces air around the center core of the engine, driven by a shaft extending from the turbine section.

The compressor, the turbine, and the bypass fan have a similar construction. They each have a rotor assembly included in a rotor disk and a set of blades extending radially outwardly from the rotor disk. The compressor, the turbine, and the bypass fan share this basic configuration. However, the materials of construction of the rotor disks and the blades, as well as the shapes and sizes of the rotor disks and the blades, vary in these different sections of the gas turbine engine. Each rotor blade includes an airfoil and a dovetail at its root, with the dovetail being radially retained in a complementary slot in the perimeter of the disk. The dovetails must be suitably configured and sized for supporting the blades with a suitably low level of stress for obtaining a useful life in operation.

In some gas turbine engine designs, the conventionally known radius ratio and blade solidity are such that the blades are disposed relatively close together around the perimeter of the disk, with the disk being relatively small in diameter compared to the airfoils which results in the inability of conventional dovetail designs to carry centrifugal loading at suitable levels of stress for enjoying a useful service life. Accordingly, the airfoils are manufactured integrally with the disk in a one-piece component conventionally known as a bladed disk or a blisk, also sometimes known as an “integrally bonded rotor” or IBR. A blisk is typically manufactured from a one piece solid forging which is conventionally machined using either a mill or electrochemical machining (ECM) electrodes. With the blades being integral with the disk, satisfactory levels of stress may be obtained in the blisk during operation for obtaining a useful life.

The primary technique for making fan blisks that are aeromechanically stable is to increase the relative thickness of the blades. The thickness is measured in thickness divided by chord, or tm/c. As a result of the increased thickness of the blades, the airfoil must support more weight, thus the thickness of the blisk and fan case are likewise increased in order to provide adequate support for the extra airfoil material. As a result of the increased tm/c, the engine may experience performance penalties.

A continuous shroud in a blisk poses numerous manufacturing problems since the shroud itself significantly limits access to the region of the inner airfoils and inner diameter of the shroud itself which are formed by removal of material from the original solid forging. In order to reduce the drawbacks associated with continuous shrouds on blisks, part span shrouds are used on bladed designs. In this arrangement, the blades are separate and attached to the blisk with dovetails. Often dovetail stresses from a bladed design are too high for a feasible design, and the engines may utilize hollow and hybrid blades for weight reduction. However, hollow and hybrid blades suffer from the drawback that these parts are expensive, and have larger tm/c values for the stability margin. Further, the hollow and hybrid blades are also not practical for medium sized engines. Further still, manufacturing challenges prevent the part shrouds from being used on blisks.

Therefore, what is needed is a fan blisk with an integral part span shroud that avoids weight and performance penalties associated with a conventional non-shrouded blisk. The present invention fulfills this need, and further provides related advantages.

SUMMARY OF THE INVENTION

One embodiment of the present invention is directed to a fan blisk including a disk, a plurality of circumferentially spaced apart airfoils extending radially outwardly from the disk where each airfoil is secured to the disk, and a plurality of shroud segments where each shroud segment is disposed circumferentially between the plurality of airfoils and is configured to attach to a corresponding airfoil of the plurality of airfoils. Further, each shroud segment of the plurality of shroud segments is attached to a corresponding airfoil by weld connections in areas along the airfoil that avoid high stress.

Another embodiment of the present invention is directed to a method for a fan blisk including the steps of securing a plurality of blade airfoils to a disk and securing a plurality of shroud segments to the plurality of blade airfoils. Further, the plurality of shroud segments are part span shroud segments that span at least a portion of the distance between adjacent blade airfoils.

Yet another embodiment of the present invention is directed to a method for a fan blisk including the steps of providing a solid piece of metallic material, machining the piece to form a disk having a plurality of circumferentially spaced apart airfoils extending radially outwardly from the disk, each airfoil being secured to the disk and having a plurality of shroud segments that are part span shroud segments that span at least a portion of the distance between adjacent blade airfoils.

One advantage of the present invention is the increased aeromechanical stability of the blisk apparatus by use of a part span shroud.

Another advantage of the present invention is the reduced thickness of the airfoils, reducing weight and improving blisk aerodynamic performance.

Another advantage of the present invention is the location of the shroud welds that avoid the high stress areas of the blisk, which increases the reliability of the apparatus.

An additional advantage of the present invention is improved fan efficiency, avoided weight penalties, and an improved stall margin as compared to an unshrouded blisk.

Another advantage of the present invention is that the apparatus functions substantially as an unshrouded blisk, having the benefits of easier maintenance, but with the performance advantages set forth above.

Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of the part span shroud on a fan blisk, according to an embodiment of the invention.

FIG. 2 is an alternative view of the fan blisk of FIG. 1.

FIG. 3A is a perspective view of an alternate welding configuration on the part span shroud of a fan blisk according to the embodiments of the invention.

FIG. 3B is a front view of the part span shroud of FIG. 3A.

FIG. 4 is a perspective view of an alternate embodiment of the invention.

FIG. 5 is an alternate view of the embodiment of FIG. 4.

FIG. 6 is an alternate view of the embodiment of FIG. 4.

FIG. 7 is an illustration of an alternate embodiment of a part span shroud welding configuration.

FIG. 8 is an illustration of the present invention with only one weld connection.

FIG. 9 is an illustration of the present invention with a weld connection substantially parallel to the shroud interface.

FIG. 10A is an illustration of the present invention where the airfoils are attached in pairs.

FIG. 10B is an alternate view of FIG. 10A where the shroud segments are connected before the airfoils are attached to the blisk.

Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1, 2, 3A and 3B illustrate various embodiments of the present invention. The present invention is directed to a part span shrouded blisk 10 that increases the stability of a fan blade while decreasing the overall weight associated with higher stability blisks. FIG. 1 shows a blisk 10 according to an embodiment of the invention showing shroud segments 18 disposed between airfoils 16 with weld connections 20 disposed substantially parallel to each other and in areas of lower stress on the part span shroud. The part span shroud segments 18 are secured with the weld connections 20 such that the weld connections are in a full line of sight and closer to the airfoils 16. The weld connections at this location on the shroud segments 18 provides a clear line of sight for implementing the weld connection, which creates an easier installation and implementation of the shroud segments 18 and weld connections 20 on the airfoils 16.

FIG. 2 shows a prospective view of the blisk 10 according to an embodiment of the invention showing shroud segments 18 disposed between airfoils 16 with weld connections 20 disposed at approximately halfway between the airfoils 16. With the weld connection 20 placed at this location, the weld is away from the fillet where the airfoil 16 meets the part span shroud. FIG. 3A shows another prospective view a blisk 10 according to an embodiment of the invention showing shroud segments 18 disposed between airfoils 16 with weld connections 20 disposed between the airfoils 16 such that the weld connections 20 are substantially parallel to each other, but offset from the center of the area between the airfoils 16 to facilitate the weld process. FIG. 3B shows a front view of a blisk 10 configuration according to one embodiment of the invention showing shroud segments 18 disposed between airfoils 16 with weld connections 20 disposed where the shroud segments 18 attach to the airfoils 16.

Referring to FIGS. 1, 2, 3A and 3B, the blisk 10 includes a disk 12 or disk body, and a plurality of circumferentially spaced apart blade airfoils 16 extending integrally radially outwardly from the disk 12. A plurality of shroud segments 18 are disposed circumferentially radially between the blade airfoils 16, and connect thereto to increase the aeromechanic stability of the blades 16 on the blisk 10. A welded connection 20 secures each of the plurality of shroud segments 18 to the blade airfoils 16 and to the other shroud segments 18. The weld connections 20 on the shroud segments 18 may include attachments resulting from welding processes including but not limited to, electron beam welding, laser welding, friction stir welding, induction welding, solid state welding and diffusion bonding and are located on the shroud segments 18 to avoid high stress areas. In addition, a plurality of coated wear surfaces 22 are disposed between the shroud segments 18 to prevent excessive wear on the shroud segments 18. The excessive wear on the shroud segments 18 can occur during operation of the blisk, when vibrations caused by the rotation of the disk 12 and blades 16, causing the shroud segments 18 to rub against each other. The disk 12, airfoils 16, shroud segments 18 and weld connections 20 collectively form an integral or one-piece assembly.

FIGS. 4, 5 and 6 are side views of a portion of a blisk 10 according to another embodiment of the present invention with the part span shroud segments 18 connected to the blades 16. FIG. 4 shows a front view of a blisk 10 configuration according to one embodiment of the invention showing shroud segments 18 disposed between airfoils 16 with weld connections 20 disposed where the shroud segments 18 attach to the airfoils 16. FIG. 5 shows an angled front view of a blisk 10 configuration according to one embodiment of the invention showing shroud segments 18 disposed between airfoils 16 with weld connections 20 disposed where the shroud segments 18 attach to the airfoils 16. FIG. 6 shows a rear view of a blisk 10 configuration according to one embodiment of the invention showing shroud segments 18 disposed between airfoils 16 with weld connections 20 disposed where the shroud segments 18 attach to the airfoils 16. The blisk 10 includes in accordance with the present invention a plurality of discrete part-span shroud segments 18 each disposed circumferentially between and bridging a respective pair of blade airfoils 16. The welded connections 20 of the shroud segments 18 to the blade airfoils 16 are disposed in areas that avoid the high stress areas of the shroud segments 18.

One embodiment of the present invention includes a method for making the blisk 10 according to the present invention by attaching the blade airfoils 16 to the disk 12 first, and then securing the shroud segments 18 to the blade airfoils 16 after the airfoils 16 are secured. The blade airfoils 16 may be attached to the disk 12 by any suitable attachment method known in the art, including but not limited to translation friction welding, electron beam welding, induction welding, solid state welding and forming the disk 12 and airfoil from the same piece of material. The blade airfoils 16 and the shroud segments 18 may be attached by a weld connection 20 with a modified shroud interface orientation, which provides a more producible weld during the assembly of the present invention. Another suitable location for the weld connection 20 on the shroud 18 may be closer to the airfoils 16, which provides better interfaces with the adjacent shroud, and provides better shroud-to-shroud interface alignment.

An alternate embodiment of the present invention is where the shroud segments 18 are integral with the blade airfoils 16. The blade airfoils 16 are secured to the disk with translational friction welding or any other suitable attachment process. The shroud segments 18 are coated with a coating known in the art for blade airfoil 16 surfaces. For example, the coating may be made of tungsten carbide, or may be a brazed on wear pad. This embodiment may also include having every other shroud segment 18 split into a plurality of shroud segments, preferably two segments. The blades 16 are then secured one at a time to the disk with translational friction weld connections. The adjacent blades 16 need to be elastically bent out of the way during the translational friction weld process to avoid interference. While no shroud welds are necessary for this configuration, alternatively, induction welding or some other joining method may be used to attach the integral blade to the blisk hub.

Another alternate embodiment of the present invention is shown in FIG. 7, where the blade airfoils 16 have two sections, a first section 24 and a second section 26, with a connection junction 28 between the two. Each of the first section 24 and second section 26 being airfoil components, when joined at the connection junction 28 forming a full airfoil. The first section 24 of the airfoils 16 is attached to the disk 12 or machined integral with the disk 12 first. Then the part span shroud segments 18 are attached to the first section of the airfoils 16, then the second section 26 of the airfoils 16 are attached last. The attachments are made by machining the first section 24 of the blades 16 and the shroud segments 18 to the disk 12, then using a weld connection 20 to attach the second section 26 of the blade airfoils 16. Another attachment used for this embodiment is to machine the first section 24 of the blade 16, then using weld connections 20 for securing the shroud segments 18 and the second sections 26 of the blade. This process is repeated around the disk 12 to form a blisk. This embodiment allows for easy attachment of the shroud segments by conventional welding techniques.

Yet another embodiment of the present invention is shown in FIG. 8, where only one weld connection 20 is applied to the shroud segments 18. The weld connection 20 is applied substantially perpendicular to the edge of the shroud segment 18. A gap clearance must be maintained from the adjacent shroud 18 without the weld connection during application of the weld 20. The shroud segment 18 without the weld may be either removed or deflected during the welding process if necessary. The gap clearance provides clearance from the adjacent airfoil and shroud during translation friction welding the airfoil 16 to the hub.

Another embodiment of the present invention is shown in FIG. 9, where a weld connection 20 is placed on the shroud 18 substantially perpendicular to the airfoil 16. The weld 20 is substantially parallel to the shroud interface between the shroud segments 18. Line 90 illustrates the direction of translation for the translation friction weld process of this configuration. The airfoils 16 may be deflected during the weld process for clearance from the adjacent airfoil. This configuration assumes a tolerance substantially perpendicular to the axis of translation of the shroud 18 and avoids welds in the shroud.

FIG. 10A illustrates another alternative configuration of the present invention. The airfoils 16 are attached to the disk 12 in pairs, or two at a time. The shroud segments 18 are coated with a wear coating at every other interface only since the blade airfoils 16 are attached two at a time. In addition, every other shroud segment 18 has a clearance gap for the translational friction weld clearance. The shroud 18 is only disposed there to avoid aeromechanic excitation from non-uniform wake disturbance. The shroud segments 18 are joined before the pair of blade airfoils 16 are attached to the disk 12, as shown in FIG. 10B.

Another embodiment of the present invention is to utilize weld connections 20 for the shroud segments 18 and the blade airfoils 16, but leaving gaps between the shroud segments. The shroud-to-shroud gap has an assembled wear surface between the two shroud pieces. This shroud-to-shroud gap provides damping during blade vibrations and prevents hoop stresses that occur in when the shrouds are connected as a continuous ring. The wear surfaces 22 are secured after the shroud segments 18 and blade airfoils 16 have been secured. This is repeated around the disk 12 to form the blisk 10.

Yet another embodiment of the present invention is to leave a gap between the shroud segments 18 and assembling a type of wear surface 22 to fit in the gap. This embodiment provides the option for not using a weld connection 22 to secure the shroud 18 to the blade airfoil 16. This embodiment provides the stiffness the airfoils require for operation, and also increases the first flex frequency. In addition, the gap provides blade-to-blade damping that reduces stresses in the shroud and blade airfoils 16. Also, the process of leaving the gap between the shroud 18 and then later assembling the wear surface in the gap provides easier assembly of the apparatus, as the shrouds 18 are not in danger of making contact with one another during the welding process.

Another embodiment of the present invention is to machine the entire blisk 10 apparatus from one material, using no weld connections 20. The blisk 10 is manufactured from a metal material such as titanium or any other suitable metal material. The shrouds 18 can be machined integrally to the airfoils as one solid piece, and form a continuous ring. In this embodiment, a wear surface 22 may be omitted. In addition, the shroud 18 could be machined as one solid piece, but each shroud segment 18 may have a gap where the gap is sufficiently large to ensure that the edges of the shroud 18 do not contact each other. A wear surface 22 can also be used that is assembled to fit into the gap between the shroud segments 18 to provide damping. As in the other embodiments, the gap eliminates any hoop stresses on the shrouds 18 and blade airfoils 16. The shroud 18 provides aeromechanical stiffness to the blade airfoils 16. Machining the blisk 10 from a single solid piece eliminates the need for wear surfaces 22.

Another embodiment of the present invention would be to construct the part span shrouded blisk 10 using composite materials and composite manufacturing techniques. The blisk 10 may be constructed of natural fiber substrates, fiberglass substrates, open cell foams, closed cell foams, vinyl, and any other suitable composite. The composite manufacturing techniques may include resin transfer molding, filament winding, autoclaving, pultrusion, hot pressing, wet layup, carbon pyrolysis, braiding or any other suitable technique. Characterization capabilities include ultrasonics, acoustic emission, X-radiography, infrared thermography, eddy current, thermal analysis, microscopy and any other suitable characterization. Composite materials performance is evaluated with a comprehensive array of testing equipment such as servo-hydraulic and screw-driven load frames, a high-rate servo-hydraulic load frame with high speed laser flash video recording, high temperature creep frames, an instrumented drop-weight impact tester, environmentally-controlled wear testers, a vacuum-ready flywheel spin chamber and any other suitable evaluation method or system.

While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. 

1. A fan blisk comprising: a disk body having a substantially circular geometry; a plurality of circumferentially spaced apart airfoils extending radially outwardly from the disk body, each airfoil being secured to the disk body; a plurality of shroud segments, each shroud segment being disposed circumferentially between the plurality of airfoils and configured to attach to a corresponding airfoil of the plurality of airfoils; and wherein each shroud segment of the plurality of shroud segments is attached to a corresponding airfoil by weld connections in areas along the airfoil that avoid high stress.
 2. The fan blisk of claim 1, wherein the plurality of shroud segments include part span shroud segments attached thereto.
 3. The fan blisk of claim 2, further comprising a plurality of wear surfaces, wherein at least one wear surface of the plurality of wear surfaces being configured and disposed to prevent excessive wear between the adjacent shroud segments.
 4. The fan blisk of claim 3, wherein the plurality of wear surfaces include at least one of a coating, cushion, or pad to prevent excessive wear on the plurality of shroud segments.
 5. The fan blisk of claim 3, wherein the weld connections secure the shroud segments in place during non-operation and secure the wear surfaces in place to prevent excessive wear during operation.
 6. The fan blisk of claim 3, wherein the plurality of wear surfaces are attached to the corresponding airfoil by weld connections.
 7. The fan blisk of claim 2, wherein the plurality of shroud segments and the plurality of airfoils are a continuous piece that are attached to the corresponding airfoil by weld connections.
 8. The fan blisk of claim 2, wherein the plurality of shroud segments comprise individual segments that provide aerodynamic damping.
 9. The fan blisk of claim 2, wherein the weld connection is a diffusion bond.
 10. The fan blisk of claim 2 wherein the disk body, the plurality of airfoils, and the plurality of shroud segments are manufactured from a composite material.
 11. The fan blisk of claim 2 wherein the weld connection is applied substantially perpendicular to the plurality of blade airfoils.
 12. The fan blisk of claim 2 wherein alternating shroud segments are weld connected.
 13. The fan blisk of claim 2 wherein the disk body, the plurality of airfoils, and the plurality of shroud segments are manufactured from a metallic material.
 14. A method for a fan blisk comprising: securing a plurality of blade airfoils to a disk; securing a plurality of shroud segments to the plurality of blade airfoils; and wherein the plurality of shroud segments are part span shroud segments that span at least a portion of the distance between adjacent blade airfoils.
 15. The method of claim 14, wherein the steps of securing the plurality of blade airfoils to the disk utilizes a weld connection.
 16. The method of claim 15, wherein the weld connection is a diffusion bond, solid state welding technique or a translational friction welding technique.
 17. The method of claim 14, wherein the step of securing the plurality of blade airfoils to a disk is before the step of securing the plurality of shroud segments to the plurality of blade airfoils.
 18. The method of claim 14, wherein the step of securing the plurality of blade airfoils to a disk is after the step of securing the plurality of shroud segments to the plurality of blade airfoils.
 19. The method of claim 14, wherein the step of securing a plurality of blade airfoils to a disk is machining the plurality of blade airfoils and the disk out of a solid piece of material.
 20. The method of claim 14, wherein the step of securing the plurality of shroud segments to the plurality of blade airfoils results in forming a solid ring of shrouds.
 21. The method of claim 14 wherein the step of securing the plurality of blade airfoils to a disk comprises having the plurality of blade airfoils integral with the plurality of shroud segments.
 22. The method of claim 14, further comprising: having a plurality of blade airfoils, wherein each airfoil of the plurality of airfoils has two sections, a first section and a second section; securing the first section of the airfoils to the disk before the plurality of shroud segments are secured; securing the plurality of shroud segments to first section of the plurality of airfoils; and securing the second section of airfoils after the plurality of shroud segments are attached to the first section of airfoils.
 23. The method of claim 14, wherein the step of providing the plurality of shroud segments with a coating is before the step of securing the plurality of shroud segments to the blade airfoils.
 24. The method of claim 22, wherein the coating is made of tungsten carbide, or is a brazed on wear surface.
 25. The method of claim 14, wherein the step of securing the plurality of shroud segments to the plurality of blade airfoils further comprises securing the plurality of shroud segments to the plurality of blade airfoils such that every other shroud segment in the plurality of shroud segments has a gap.
 26. The method of claim 14 wherein the step of securing a plurality of blade airfoils further comprises attaching two blade airfoils at a time to the disk, the plurality of airfoils being connected to each other at the shroud.
 27. A method for a fan blisk comprising: providing a solid continuous piece of metallic material; machining the piece to form a disk having a plurality of circumferentially spaced apart airfoils extending radially outwardly from the disk, each airfoil being formed from piece; forming a plurality of shroud segments on the airfoils wherein the plurality of shroud segments are part span shroud segments; and wherein the plurality of shroud segments are part span shroud segments that span at least a portion of the distance between adjacent airfoils. 